Sending MIDI events -- `amy.send_midi()` and/or special `synth_flags` bit?

[dpwe]

#763 sharpens the distinction between note-ons received via MIDI and amy.send(.., vel=1) note-ons.

My problems there could be solved by having a second command, amy.send_midi() that mirrors the kwargs of amy.send(), but delivers note-ons via the MIDI mechanism (with the specific implication that they are captured by any midi_note_cmds that have been set up.

But this could be a nice way to generate MIDI commands for sending out as well. Instead of midi_send([0x90, 0x40, 0x7F]), you could amy.send_midi(synth=1, note=64, vel=1).

The same mechanism could both route to internal synths and send MIDI bytes out the MIDI interface. In the spirit of "MIDI Thru", it could do both at the same time, although we could add flags to select only one or the other.

We could have channel=X as an alias for synth=X, and we could add kwargs for control=, value=, and program= to pythonically wrap different kinds of MIDI messages.

[bwhitman]

isn't this already in?

amy.send(synth=1, oscs_per_voice=1, num_voices=6, wave=amy.MIDI)
amy.send(synth=1, note=64, vel=1)

[dpwe]

That's close, but different. I don't remember, but I'm assuming wave=AMY_MIDI builds a synth where sending notes to the synth just generates MIDI events on the corresponding channel, to provide a mechanism for sending MIDI out of the AMYboard that looks like normal triggering. So if you have an outboard synth on MIDI channel 8 and you want to switch between sending notes to that vs. sending notes to an internal synth, you can set them both up, then alternate the synth you send the note events to.

amy.send_midi() generates MIDI events without reference to whether an internal synth has been set up on that channel. So even if synth 1 exists, amy.send_midi(synth=1, ...) will send a MIDI event out the MIDI port. But it will also pass that event through the MIDI input mechanism, so if there is an internal synth 1 (and it has grab_midi_events true), it will receive the note on.

What's the difference? It's about the handling of MIDI drums. Right now a channel 10 MIDI event for note 39 translates into sending a note-on for note 94 to a wave=PCM osc configured with preset 9. Doing amy.send(synth=10, note=39, vel=1) is internally translated to an amy_event with midi_note=94, wave=PCM, preset=9, vel=1.

Having amy.send_midi() would allow you to send the pre-translation messages (note=39), while still preserving a path to drive the post-translation messages (note=94) (via plain amy.send()).

Basically, under my current proposed branch, amy.send(synth=10, note=KICK, vel=1) would stop working (because it's expecting note=94 and a preset to be specified) -- even though incoming MIDI events on Chan 10 are handled correctly. So I'm proposing to add a new function so that amy.send_midi(synth=10, note=KICK, vel=1) will work instead.

[dpwe]

It turns out that wave=amy.AMY_MIDI sets up an osc where note events sent to that osc have no effect on the output waveform but instead cause a MIDI note event to be emitted (via amy_midi.c:amy_send_midi_note_on(osc). This feels odd, since the parameters are mediated by the synth[osc] structure, but it's also deficient in that the MIDI channel cannot be specified (so events are always sent on channel 1).

It makes more sense to use synth objects when commanding MIDI output (since we already use synth=X to indicate the incoming MIDI channel).

I propose to define a new synth_flag bit to indicate ".. and echo this event on MIDI_OUT." If set on a synth with no audible oscs, this would be a purely "send this event to the output MIDI" synth, but it could also be set on active synths, to have its events echoed to MIDI out.

A "silent" MIDI_OUT synth would, however, probably need to have one osc allocated, because we generally use zero oscs as a flag to delete a synth altogether. Maybe we should define a new patch number for "MIDI out synth", so you can say amy.send(synth=X, patch=amy.MIDI_OUT_PATCH, num_voices=1). (Ideally, I'd like to get rid of obligatory num_voices, have it default to 1.)

This change will break any existing use of wave=amy.AMY_MIDI. I'm not aware of anywhere that is being used. The description in docs/midi.md will need updating.